1. Field of the Invention
This invention relates generally to a substantially non-irritating oral composition, and more particularly, to a non-irritating oral composition exhibiting high foaming properties and stable rheology.
2. The Prior Art
Sodium lauryl sulfate (SLS) is a widely used surfactant in oral compositions. Surfactants, and particularly anionic surfactants such as sodium lauryl sulfate are an essential ingredient of oral compositions and serve as a solubilizing, dispersing, emulsifying and wetting agent for the other ingredients present in the dentifrice and is especially effective in solubilizing the flavor present. A cosmetic effect of the presence of the surfactant is that it promotes foaming of the oral composition. Oral compositions with strong foaming ability are preferred by consumers since the foaming provides the perception that the oral composition cleans effectively only if it foams well.
The incorporation of anionic surfactants such as sodium lauryl sulfate in oral compositions such as dentifrices is known to cause adverse reactions to oral tissue such adverse reactions being reported in R. C. Caldwell and R. E. Stallard, A Textbook of Preventive Dentistry, 196, W. B. Saunders (1977); L. J. Guarnieri, IADR, Abstract No. 661 (1974); L. J. Guarnieri, Thesis, University of Indiana (1970). One example is gingival irritation. It is also believed that sodium lauryl sulfate is responsible for sloughing of the oral mucosa.
The art therefore has been seeking a non-irritating alternative to sodium lauryl sulfate as an anionic surfactant for dentrifrices.
U.S. Pat. Nos. 4,690,776 and 5,041,280 disclose the use of the anionic surfactant sodium lauryl sulfoacetate in dentrifrice formulations. However, the problem of oral irritation due to the presence of anionic surfactants in the dentifrice is not mentioned in the aforesaid patents.
According to the published literature; namely, "Surfactants in Cosmetics (Marcel Dekker), Vol. 16, Ch. 10, Pages 303-304 (1985), sodium lauryl sulfoacetate is of comparatively little importance commercially in oral hygiene products. According to this publication, although the use of sodium lauryl sulfoacetate has been proposed as a foaming agent in dentifrices and other dental preparations, it is not considered as an organoleptically acceptable product for commercial applications.
Attempts to use commercially available sodium lauryl sulfoacetate as a surfactant in oral products such as dentifrices indicate the problem of a bitter taste associated with the presence of the compound in the oral product. Further, compared to sodium lauryl sulfate, dentifrices employing sodium lauryl sulfoacetate as the surfactant exhibit inferior foaming properties. Copending patent application U.S. Ser. No. 07/908,104 Filed Jul. 2, 1992, discloses that dentifrices formulated with a purified form of sodium lauryl sulfoacetate, that is, one having admixed therewith less than 18% non-dodecyl sulfoacetate impurities is organoleptically pleasing when compared to dentifrices formulated with the commercially available unpurified sulfoacetate compound.
Further work in preparing dentifice formulations in which the purified sodium lauryl sulfoacetate is incorporated indicates that on storage in a tube or other similar container the sodium lauryl sulfoacetate forms a lamellar and liquid-crystalline structure with the result that the viscosity of the dentifice is elevated to a level that the product cannot be readily extruded from the tube or similar container rendering the product unacceptable for consumer use. Attempts to alleviate this viscosity elevation problem by including a nonionic co-surfactant in the dentifice at a concentration sufficient to provide acceptable rheology has been found to have the disadvantage of imparting either inferior foamability to the dentifice or an unacceptable bitter taste to the product.
There is therefore a need in the art involving the utilization of purified sodium lauryl sulfoacetate as a surfactant in dentifrices that the problem of unacceptable viscosity change of the stored product be alleviated without deleteriously affecting the foamability or taste of the product.